The present invention relates generally to water or sewage settling tanks and particularly to an improvement in the settling tank and floating siphon system for removing sludge from the bottom of the tank as shown in my U.S. Pat. No. 3,333,704, issued Aug. 1, 1967. The operation of settling tanks is well known in the art. Briefly, the liquid to be treated is introduced at one end of the tank while the clarified liquid is removed from the other end. As liquid travels from the inlet to the outlet, under conditions of non-turbulent flow, solids settle out of the liquid and on to the bottom of the settling tank. Various devices are employed for removing the solids from the bottom of the settling tank, one such device being that siphon system illustrated in my patent.
Settling tanks for treating municipal or industrial water supplies or sewage waste are relatively large and it is not unusual for such tanks to be 10 to 12 feet deep. Consequently, the tank must be relatively long or flow must be relatively slow in order to permit ample time for the solids and fine materials to settle the full vertical height of the tank on to the bottom before the liquid leaves the tank outlet. While the settling rate could be increased, and the efficiency of the tank improved by decreasing the depth of the tank, this heretofore could not be economically accomplished and still maintain the required tank capacities.
Plate settlers are known in which a plurality of closely spaced horizontal plates are placed within the tank. Here the plates are either placed at a slight incline so that sludge may move down the plates by gravity to a removal trough or, in some cases, the plates are movable so they can all be tilted as a unit for removing the sludge. The use of a siphon system as illustrated in my U.S. Pat. No. 3,333,704 to remove sludge from such plate settlers is not practical for two reasons. First, some provision must be made to permit the siphon inlet to extend both the full vertical height of the tank and to move the full length of the tank. For this reason, there can be no plate which extends the full width of the tank. Secondly, there can not be any support structure between the vertically spaced plates which would interfere with the free passage of the siphon inlet over the entire plate surface of all the plates.
According to the present invention, even existing settling tanks can be easily and economically modified so as to provide a multi-level tank which decreases the settling distance and therefore the settling time and which utilizes a floating siphon system that provides an efficient means for removing the settled materials from each tank layer.